I'm thinking of ditching my front swaybar and adding more front spring rate in the quest for weight loss on my Si, and perhaps (actually, the primary reason) even get it to handle better as no front swaybar seems to work for a lot of people. Thoughts? The car weighs a hair under 2400 right now. I'm thinking I should at least figure out approximately how much more rate I would need in the front to compensate for the lack of contribution from the swaybar because I don't want to get any softer in roll than I am now.

Current setup is stock 26mm front bar, 22mm Comptech rear, 600/800 with SPSS Konis, this is an SCCA DSP autocross car

 

I calculated the bar rate at around 566 lbs/in (as in, apply opposing forces of 566 lbs. to each end, and each side will deflect 1 inch). That assumes rigid bushings, so taking that and the different motion ratios into account, my best guess would be that you'd need to increase your front spring rate by about 250 lbs/in.

Now, is it a good idea? I'm doubtful, but I done thinking for tonight, so that's all you get.

 

Yeah, I saw your bar post in the other thread and that was a mouthful.

I'm just struggling to even find places to lose much weight in this car without any update/backdate options . Yeah, I can lose some wheel weight, some suspension weight, some interior weight but none of that is really off the nose and none of it is much at all. I suppose handling is important...I guess...maybe.

 

This thing is in danger of vanishing into the dark depths of the 2nd-last pages, so I'm posting in it again. Still want to talk to you people about this idea.

 

just run it without the front bar with your current setup......use throttle oversteer.

If you don't like it then try a smaller bar.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by TeamSlowdotOrg &raquo;</TD></TR><TR><TD CLASS="quote">This thing is in danger of vanishing into the dark depths of the 2nd-last pages, so I'm posting in it again. Still want to talk to you people about this idea. </TD></TR></TABLE>
I'd like to know also... for that matter, the effective rate of the rear bar would be nice to know also.

Christian, who probably needs more rear spring and less rear bar

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by B HATCH &raquo;</TD></TR><TR><TD CLASS="quote">just run it without the front bar with your current setup......use throttle oversteer.

If you don't like it then try a smaller bar.</TD></TR></TABLE>

yeah.. it'll be a big difference, but I'd try it out..

I'm still not running a front bar on my R, with OEM shocks and springs(one change at a time here).. I like it a lot, but there's a lot of roll.. I need stiffer front springs for sure..

12k/8k is probably what I will end up with, which I think will end up dialing back out some of the oversteer I experience now(althought I like it and will probably make adjustments to bring some back)..

&lt;-- still learning about suspension theory, so I wouldn't be surprised if the last part was just plain wrong..

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by B HATCH &raquo;</TD></TR><TR><TD CLASS="quote">just run it without the front bar with your current setup......use throttle oversteer.</TD></TR></TABLE>

wtf is "throttle oversteer" on a FWD car?

 

Here's my central question: Would disconnecting the the stock front bar, combined with the use of stiffer springs to offset the lost roll stiffness, do anything to make the car extremely weird? Is there anything fundamentally wrong with how I'm thinking about it? Because if there is... *shakes fist*

I'd love to drop the weight off the nose, and my car can benefit from some more rotation but that I plan to solve in other ways. My main goal is not to adversely affect anything.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Tyson &raquo;</TD></TR><TR><TD CLASS="quote">wtf is "throttle oversteer" on a FWD car?</TD></TR></TABLE>I was just wondering that myself, maybe he's talking about "OH NOES OVERSTEER MASH THE GAS OR WE DIE" oversteer, which is oversteer during which the throttle is used to prevent sudden heart stoppage due to decapitation.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Tyson &raquo;</TD></TR><TR><TD CLASS="quote">wtf is "throttle oversteer" on a FWD car?</TD></TR></TABLE>


Possibly "snap throttle oversteer"??? Steady state cornering, get off the gas, rotate, back on... Just a thought.

 

"throttle oversteer"? probably another term for lift/drop throttle oversteer which has like 300 names, all of which are dumb. =&gt; when you're on the throttle and turning you lift, unloads rear tires, and rear end comes a swingin'.

The problem with "exchanging" rollbar rate for springrate is that a rollbar doesn't add rate linearly. I explained it in the other post somewhat, but basically the spring force = k1*x, where x is deflection, while bar force = k2*l*cos(angle), where l is moment arm. The stiffer you springs, the less of an issue this is and they end up equal as the stiffness k1 and k2 approach infinity (ooops solid suspension). I think something like this isn't that important for an autocross car, but probably considered by Formula 1, which I dont' believe the Civic Si is currently classed for.

You can equate your roll going from spring+bar to spring (ignoring the crap above), but you will experience balance differences, based on the fact that your front bar doesn't do anything under lognitudinal chassis differences. More equally loaded tires allows more front grip with no sway, but there will be less compliance for rapid transitions...which is maybe why some say a car with no front bar has shitty turn-in?

 

A little more pertinent info: my front suspension (this is through testing with zip-ties) compresses a maximum of 1.25", ever, and that was a big big bump. Normally it only uses 1" of travel at an autocross.

I think I need to try it, or at least try disconnecting it the next time I drive my car.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by TeamSlowdotOrg &raquo;</TD></TR><TR><TD CLASS="quote">Here's my central question: Would disconnecting the the stock front bar, combined with the use of stiffer springs to offset the lost roll stiffness, do anything to make the car extremely weird? Is there anything fundamentally wrong with how I'm thinking about it? Because if there is... *shakes fist*

</TD></TR></TABLE>

No, diconnecting the front swaybar will not cause any weirdness unless your suspension is riding the bump stops. Since most Front bars are soooo small in diameter, it wouldn't take a much larger rate spring in the the front to offset the loss of front roll stiffness.

 

*Most* stock front bars are small, but mine's pretty large, about the same as an ITR's. This isn't a change I'll be trying until after Nationals (assuming I end up not finding a ride), but it's something I'm thinking would give the important weight loss benefit without adversely affecting handling, unless I'm just thinking of it all wrong, which is what I'm waiting for the many know-more-than-me's on here to tell me.

That's one vote no and one vote yes, I suppose.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by GSpeedR &raquo;</TD></TR><TR><TD CLASS="quote">
The problem with "exchanging" rollbar rate for springrate is that a rollbar doesn't add rate linearly. I explained it in the other post somewhat, but basically the spring force = k1*x, where x is deflection, while bar force = k2*l*cos(angle), where l is moment arm. The stiffer you springs, the less of an issue this is and they end up equal as the stiffness k1 and k2 approach infinity (ooops solid suspension). I think something like this isn't that important for an autocross car, but probably considered by Formula 1, which I dont' believe the Civic Si is currently classed for.

You can equate your roll going from spring+bar to spring (ignoring the crap above), but you will experience balance differences, based on the fact that your front bar doesn't do anything under lognitudinal chassis differences. More equally loaded tires allows more front grip with no sway, but there will be less compliance for rapid transitions...which is maybe why some say a car with no front bar has shitty turn-in?</TD></TR></TABLE>

The bar rate is virtually linear even with the cos(lever arm angle) term since it is the change in the cos() term (i.e. cos(lever arm angle static) - cos(lever arm dynamic) that you have to follow. Let's say that the static anti-roll bar lever arm angle is say 15 degrees (to horizontal) and the dynamic angle is 25 degrees, the difference in the lever arm length is only 6% over the 10 degrees of anti-roll bar rotational deflection. This is not enough of a non-linearity to be concerned with IMO.

 

Having a 26mm bar is certainly adding a lot of roll stiffness to your car. The most important thing is what is your car currently doing in the corners. Is it pushing at corner entrance (A sign the front roll stiffness or compression damping is too high) what about mid corner, and lastly exit? These are the questions that you need to answer before you can determine any kind of suspension setup.

 

It's not doing anything wrong right now. Maybe a hint of push everywhere, but I'm going to solve that with alignment and adding some front contact patch with wider wheels under my 225's before trying to make a significant balance change with suspension components. My aim here would be to maintain the status quo for the front while losing a relatively large amount of weight off the front of the car.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Johnny Mac &raquo;</TD></TR><TR><TD CLASS="quote">Is it pushing at corner entrance (A sign the front roll stiffness or compression damping is too high) what about mid corner, and lastly exit? These are the questions that you need to answer before you can determine any kind of suspension setup.</TD></TR></TABLE>

My car pushes at exit. Mid corner is a bit loose... stock suspension, installing a 25mm rear swaybar soon.

 

Any idea what the rate of the front bar is? I can't imagine it's nearly as high with all the crooks and bends.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by bfitz &raquo;</TD></TR><TR><TD CLASS="quote">I calculated the bar rate at around 566 lbs/in (as in, apply opposing forces of 566 lbs. to each end, and each side will deflect 1 inch). That assumes rigid bushings, so taking that and the different motion ratios into account, my best guess would be that you'd need to increase your front spring rate by about 250 lbs/in.

Now, is it a good idea? I'm doubtful, but I done thinking for tonight, so that's all you get. </TD></TR></TABLE>

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Johnny Mac &raquo;</TD></TR><TR><TD CLASS="quote">The bar rate is virtually linear even with the cos(lever arm angle) term since it is the change in the cos() term (i.e. cos(lever arm angle static) - cos(lever arm dynamic) that you have to follow. Let's say that the static anti-roll bar lever arm angle is say 15 degrees (to horizontal) and the dynamic angle is 25 degrees, the difference in the lever arm length is only 6% over the 10 degrees of anti-roll bar rotational deflection. This is not enough of a non-linearity to be concerned with IMO.</TD></TR></TABLE>

Based on a (somewhat conservative) 4" effective arm length for a front bar, and a maximum suspension compression of 1.5" (based on 850lb or so with 600# front springs), the sway rotates about 21 degrees. This increases the difference to ~8% over the total range, which I'll agree isn't a large amount. Like I said, more significant with softer springs.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">Any idea what the rate of the front bar is? I can't imagine it's nearly as high with all the crooks and bends.</TD></TR></TABLE>

Ony considering the moment arm (perpendicular to the main bar axis) is a decent approximation. Otherwise you need to look at different torsion values due to stress concentrations.

Edit: max compression will actually be more than 1.5" since I forgot to think about WT. I don't want to calculate it anyway.


Modified by GSpeedR at 8:45 PM 8/4/2004

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by GSpeedR &raquo;</TD></TR><TR><TD CLASS="quote">"throttle oversteer"? probably another term for lift/drop throttle oversteer which has like 300 names, all of which are dumb. =&gt; when you're on the throttle and turning you lift, unloads rear tires, and rear end comes a swingin'.
</TD></TR></TABLE>

Yes.......

Lift and the *** gets loose (but on a FWD you also loose tire force cause you using some tire for back driving the engine). Power on to get the *** planted, same as RWD but on FWD it lifts weight off the drive wheels.

 

I believe Brian was talking about the front bar, since that's what I asked about.

 

I would think that your car pushes too much with such a thick front sway bar. Remenber that bar stiffness goes up as the fourth power of diameter, so a 26 mm bar is 1.95 times stiffer (let's say twice as stiiff) than a 22 mm bar. While you can certainly remove or disconnect the bar (rear end will be more apt to come around), and up the springs to compensate, you might just try a smaller front bar. It won't take more than a couple of pounds off, but it should help the car rotate much better. Then you can think about a larger rear bar to make the car rotate even more, and get back your original roll stiffeness. Each time you make a change you will have to re-determine your optimum alignment.

 

That's the thing, I'm most concerned about ditching that weight without hurting the balance because we all know my car is a fat pig, and running without a front swaybar, if it's not a horrible idea as far as handling goes, would be a great way to lose that weight for what amounts to free. If I know I'm at least not completely off-base by thinking I can get away with ditching the front bar and upping the spring rates to get the car lighter and still handle the same, I'll do it. The balance is acceptable right now, but I'm going to try a few things to give the car more front grip without sacrificing rear grip.

 

By throwing on a smaller front and larger rear bar, how would front/rear roll stiffness be the same (since you don't combine them) as before unless you lowered the rear spring rate? Real roll stiffness increases.